The present invention relates to the fabrication of metallic components, and more particularly to a novel parts orbiter for use in a chem-milling vat.
The orbiter will generally be described with reference to producing chemically milled external isogrid or waffle grid patterns on a circular or non circular symmetrical shell structure. Such integral titanium or Inconel structures are found in aircraft engine inlets, by pass ducts and augmenter cases. The orbiter, however, is not limited by the construction material, to any set of structural shapes or applications, to whether the structure is pocketed or not and, when it is pocketed, to any specific type or configuration of pocket or grid pattern.
An orbiter, as it applies to chem-milling processes, is typically used to control the movement or tumbling of a part or a collection of parts in an etchant bath in such a manner that, in effect, the part or parts receive uniform exposure to the etchant and therefore receive uniform chemical milling. This typically requires that all exposed (i.e. chemically milled) surfaces spend an effective equal amount of time in varying positions with respect to the gravitational vertical. The following paragraphs explain and identify the phenomena influencing the above preferred (ESIO) exposed-surface integrated orientation and the manner in which applicant's orbiter provides the unique, singular and universal means for optimizing the (ESIO) exposed-surface integrated orientation.
If an essentially flat pocket is inverted in a quiescent or agitated etchant bath such that the exposed surface faces downward along the gravitational vector, then the gasses or fumes generated by chemical milling will accumulate in the pocket and either inhibit or stop the chemical milling from preceeding in that pocket. The degree that the pocket is curved (in single or compound curvature) in conformance with the shell curvature and the pocket depth exceeds the local vertical pocket arc height, part (i.e. the center) of the pocket experiences dramatically different rates of metal removal than other parts (i.e. the edges) of the pocket. This condition, caused in part by the entrapment of fumes under the maskant overhangs, is particularly prevalent when the pocket is at or near a bottom dead center orientation.
Also during the periods the pockets being chemically milled have exposed surfaces in other than inverted positions the uniformity of the depth of cut, etch rates, ridging, dishing, etch factors along the pocket edges and channeling are dependent on the sum total of the times the pockets are exposed in these varying non inverted positions. As in the case of inverted pockets, these effects are also influenced by such factors as the the bath temperature thermal gradients in the etchant and part, acid and surfactant concentration levels, the degree of dissolved metal concentration in the etchant, and the heat sink created by the mass in the rib cross sections.
The knowledge of the afore mentioned and related facts in qualitative form and quantitative detail is determined from experiment or published data in the public domain is of importance, and invoked hereby reference, for implementation and utilization of applicant's novel orbiter.
The quality of chemical milling is essentially the net result of cumulative effects experienced in pockets during periods the pockets are inverted and non-inverted positions as outlined above. The means provided by applicant's orbiter for optimally controlling the part (ESIO) exposed-surface integrated orientation is the single most important factor in moderating and mitigating the outlined and related adverse phenomenological effects on chemical milling quality.
It should be noted that pockets can be formed by deliberate maskant scribing or the basic shape of the part being chemically milled. When a part in effect has no pockets then the inverted exposed surface position referred to above is a theoretical singular point and is non existant and the chemical milling anomalies which imply the existance of pockets are not operable. In such a case applicant's orbiter provides means for optimizing the (ESIO) exposed-surface integrated orientation based on the inherent part geometry, its internally or externally controlled heat sinks as well as the standard etchant formulation and control parameters.
Some patents that teach the processes for forming intricate metal structures using chem-milling are illustrated in U.S. Pat. No. 4,137,118 of Brimm and U.S. Pat. No. 3,940,891 of Slysh. The Brimm patent also discloses an early version of an orbiter.
It is an object of the invention to provide a novel parts orbiter for chem-milling that has dual drives that permit infinite orbiting ratio adjustments.
It is also an object of the invention to provide a novel orbiter for chem-milling that allows the orbiting parameters to be adjustable for longitudinal and circumferential etch factor and removal rate modifications.
It is an another object of the invention to provide a novel orbiter for chem-milling that allows taper removal to be accomplished following normal chemical milling.
It is an additional object of the invention to provide a novel orbiter for chem-milling that is economical to manufacture and market.